A multi-chip package (MCP) generally refers to an electronic package where multiple components, e.g., integrated circuits (ICs), semiconductor dies or other discrete components are packaged onto a unifying substrate. The MCP is an important facet of modern electronic miniaturization and micro-electronic systems.
A relatively new aspect of the MCP technology development is a “chip-stack” packaging. The chip-stack packaging allows the die blocks to be stacked in a vertical configuration making the resultant MCP footprint significantly smaller. Because area size is greatly valued in miniature electronics designs, the chip-stack is an attractive option in many applications, for example, cell phones and personal digital assistants (PDAs).
One of the challenges of the MCP technology is that the height of the components varies. The height variation further increases for the stacked dies. Currently, the height variation is absorbed by the first level thermal interface material (TIM1) that is applied between a die and an integrated heat spreader.
Generally, the TIMs are thermally conductive materials, which are applied across jointed solid surfaces to increase thermal transfer efficiency. The TIM1s are applied between the die and the integrated heat spreader to lower package thermal resistance.
FIG. 1A is a cross-sectional view 100 of a typical MCP having components with the same nominal height. As shown in FIG. 1A, a component 103 and a component 104 are on a substrate 101. Components 103 and 104 have the same nominal height. An integrated heat spreader (IHS) 102 is attached to a substrate 101 above component 103 and component 104. As shown in FIG. 1A, a first level thermal interface material (TIM1) 105 is applied between the die of the component 104 and IHS 102. A TIM1 106 is applied between die of the component 103 and IHS 102.
Although the components in the MCP can have the same nominal height, there is natural height variation across the components. As shown in FIG. 1A, the die height of the component 104 is greater than the die height of the component 103. As shown in FIG. 1A, TIM1 106 is thicker than TIM1 105 to compensate for the die height difference.
FIG. 1B is a cross-sectional view 120 of a typical MCP having components with different nominal heights. As shown in FIG. 1B, a component 113 represents a die mounted on a substrate 110 via a ball grid array (BGA) assembly 111. A component 114 represents a die directly attached to substrate 110. The nominal height of component 113 is greater than the nominal height of the component 114. An IHS 112 is attached to a substrate 110 above component 113 and component 114. As shown in FIG. 1B, a TIM1 116 is applied between the component 113 and IHS 112. A TIM1 115 is applied between component 114 and IHS 112. As shown in FIG. 1B, TIM1 115 is thicker than TIM1 116 to compensate for lower height of the component 114.
That is, compensation for the height variation occurs at the expense of increasing the thickness of the TIM1 between the die and the integrated heat spreader. However, thicker TIM1 bond line hurts thermal performance of the MCP that leads to limited bandwidth, frequency, greater power leakage, and the like. Additionally, absorbing the height variation by the TIM1 limits choice of TIM 1 materials.
Reduction in cooling capacity of the TIM1 significantly impacts an electronic system performance and significantly increases the risk of the component failure. As power consumed by the MCP modules and the number of the components in the modules increase, the risk of the component failure caused by the reduction of the cooling capacity of the TIM1 further increases.